1. Field of the Invention
The present invention relates to a seat-back frame for vehicles that is capable of protecting the persons sitting in the car from the shock of a rear-end collision.
2. Description of the Related Art
To soften the shock within a vehicle that is hit in a rear end collision, it is desirable that the car""s seat-back frames should move backward and rotate while absorbing the energy of the collision. Therefore, it is preferable to increase the amount of the rotation in the lower portion of the seat-back frame. However, in order to protect the vertebrae of the persons in the car during such a collision, it is desirable that the lower portion of the seat-back frame should change in shape. Therefore, the problem is that the protection of the vertebrae is insufficient when the amount of the rotation in the lower portion of the seat-back frame increases as described above, because when the amount of that rotation increases, the momentum of the rotation acts on the vertebrae. For these reasons, in a conventional seat-back frame for vehicles, the rotation of the seat-back frame is limited to a specified amount.
For example, in the VOLVO S80 vehicle, a rear-shock-absorbing system is built into the seat-reclining system. Thereby, if a rear-end collision occurs, the lower part of the seat-back frame moves backward and the upper part thereof moves forward so as to push the head forward and to hold it and thereby to protect it. Then, while the back is held by the seat-back frame, the entire seat-back frame falls backward (while pushing the head forward and holding it, so as to prevent a whiplash injury) whereby the force pushing the head forward is softened. However, if a rear-shock-absorbing system is built into the seat-reclining system, two problems result: (1) the structure of the seat-reclining system is complicated and hence is very costly; and (2) the whole seat becomes so heavy that it is difficult to handle.
However, there is a different structure such that a notch is furnished in the lower portion of the seat-back frame, and if shock results due to a rear-end collision the seat-back frame is changed in shape, with said notch being the starting point of such change. But such a structure has the problem that the load for the backward movement and rotation of the seat-back frame is inconstant, so that stable behavior is impossible.
The present invention is intended to solve the problems observed in the art. The object of the present invention is to provide a seat-back frame that, with a simple structure and without being heavier in weight than a conventional frame, is capable of protecting the passengers in a car from the shock of a rear-end collision.
In order to attain the object described above, a seat-back frame of the invention is provided, wherein, (1) the seat-back frame has right-side and left-side members that are made of sheet steel and that have a number of holes in their lower portions, (2) each of the side members is fastened to an external member (such as a seat-reclining system) by fastening bolts that are inserted in each of the holes, and (3) the fastening structure is configured so that the brims of all of the holes, or all of the holes but one, are able to make contact with their respective aforementioned fastening bolts.
If a rear-end collision occurs, a rotation-movement force acts on the seat-back frame, moving it backward. In this invention, the structure is arranged so that the fastening bolts and the brims of the holes are capable of making contact with each other, and, due to the force of the rotation of the seat-back frame, the fastening bolt moves while making contact with the brim of the hole so as to elongate the hole. Therefore, the seat-back frame is able to move backward while rotating, so that the external force of the rear-end collision is absorbed by such a movement. Thereby, the passenger sitting on the seat is protected.
In this invention, a complicated shock-absorbing system is not necessary, and the protection of a person in the seat can be secured by a seat-back frame that has a simple structure and that is not heavier than that of a conventional model.
In accordance with an aspect of the invention, the aforementioned fastening bolt for each of the holes but one is furnished with a free nut that is not welded to the side member.
In this invention, one or more of the holes of the side members are elongated by a respective fastening bolt that is furnished with a free nut. Therefore, the passenger in the car is protected by the inventive seat-back frame that has a simple structure.
In accordance with an aspect of the invention, at least one each of the aforementioned holes is placed toward the front portion of the lower part of the side member and at least one hole is placed toward the rear portion thereof, and the fastening bolt that is inserted in the front-side hole is furnished with a free nut, while the fastening bolt that is inserted in the rear-side hole is furnished with a welding nut.
In this invention, the rear portion of the side member is strongly held by the welding nut, wherefore the holding force of the hole at the front end of the side member is less than that of the hole at the back end. Therefore, when external force is applied, the front-side hole is elongated by the movement of the fastening bolt, so as to protect the person in the seat.
Also, in the operation described above, the whole seat-back frame moves backward and rotates while holding the back of the person sitting in the seat, with the lower portion of the seat-back frame as the center of said rotation, so that the protection of the vertebrae of the person is secured.
In accordance with an aspect of the invention, each side member includes a stopper flange that limits the external-force-caused movement of each fastening bolt that is attached to a free nut.
The stopper flange limits to a specified amount the forced movement of the fastening bolt that is attached to a free nut, and therefore the rotation of the seat-back frame will not exceed a specified amount. Accordingly, excessive stress does not act on the vertebrae of the person in the seat and consequently the person is protected from the force of a rear-end collision.
In accordance with an aspect of the invention, the aforementioned external member is a seat-reclining system of the seat.
Accordingly, the shock of a rear-end collision is transferred from the seat-reclining system to the side members, and the whole seat-back frame moves backward while rotating, so that the person in the seat is protected.